This invention generally relates to vascular catheters and particularly to catheters for vascular procedures such as percutaneous transluminal coronary angioplasty (PTCA).
In typical PTCA procedures, a guiding catheter having a performed distal tip is percutaneously introduced into the cardiovascular system of a patient and advanced therein until the distal tip of the guiding catheter is in the ostium of the desired coronary artery. A guidewire and a balloon dilatation catheter are introduced into the patient's vascular system through the previously introduced guiding catheter. The guidewire is first advanced out of the distal tip of the guiding catheter into the patient's coronary vasculature until the distal end of the guidewire crosses the lesion to be dilated. The dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced over the previously positioned guidewire, with the guidewire slidably disposed within an inner lumen of the dilatation catheter, until the dilatation balloon is properly positioned across the lesion. Once in position across the lesion, the flexible, relatively inelastic balloon is inflated to a predetermined size with radiopaque liquid at relatively high pressures (e.g., at least 100 psi) to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall. The balloon is then deflated so that the blood flow can resume through the dilated artery and the catheter can be removed.
Further details of angioplasty procedures and the devices used in such procedures, can be found in U.S. Pat. No. 4,332,254 (Lundquist); U.S. Pat. No. 4,323,071 (Simpson-Robert); U.S. Pat. No. 4,468,224 (Enzmann et al.) U.S. Pat. No. 4,516,972 (Samson); U.S. Pat. No. 4,528,622 (Samson et al.); and U.S. Pat. No. 4,616,652 (Simpson) which are hereby incorporated herein in their entirety.
It is generally desirable to make the deflated profile of a dilatation catheter as small as possible because a smaller profile allows the catheter to pass through tighter lesions and to be advanced much further into the patient's coronary anatomy. However, if the diameter of the guidewire is reduced in order to reduce the profile of the catheter, the ability of the guidewire to transmit torsional and axial forces is likewise reduced. Heretofore, movable guidewires utilized in coronary angioplasty typically have been on the order of 0.012-00.018 inch (0.305-0.457 mm) in diameter. Attempts have been made to use smaller diameter movable guidewires in angioplasty procedures, but such smaller diameter guidewires could not always effectively transmit torque for steering the guidewire from the proximal to the distal ends, particularly when the guidewire was disposed in the patient's tortuous coronary vasculature. Moreover, small diameter movable guidewires did not always have the pushability to be readily advanced through the tortuous coronary vasculature without buckling.
Reducing the wall thickness of the tubular members which make up the catheters, can also reduce the profile, but as with reducing the diameter of the guidewire, there is a limit on how much the wall thickness of the tubular members can be reduced without detrimentally affecting the performance of the catheter. For example, if the wall thickness is reduced to such an extent that the circularity of the inner member of a dilatation catheter cannot be maintained during the placement of the catheter within the patient's vasculature, i.e., the tubular member kinks. Any guidewire disposed within the tubular member in such a case would become bound within the inner lumen thereof and could not be further advanced. This factor is particularly important with dilatation catheters in which there are very small differences in size between the outer diameter of the guidewire and the inner diameter of the lumen in the inner tubular member, such as those described in co-pending application Ser. No. 220,563, filed Jul. 18, 1988, entitled Vascular Catheters.
What has been needed and heretofore unavailable is a dilatation catheter assembly which has a substantially reduced profile with essentially no loss in performance characteristics. The present invention satisfies that need.